The present invention is related to a filtering technique for electrically charged particles of a particle beam according to their kinetic energy performed by deflection of the trajectory of the beam. The present invention also relates to an energy filter, wherein electrically charged particles of a particle beam are filtered according to their respective kinetic energy by deflecting the propagation path of the beam and is still further related to a combination of such an energy filter with a further filter arrangement, wherein the particles of the beam are filtered according to their mass so as to form an analyser arrangement.
The present invention is further directed on an electron impact ionization source of the kind where neutral particles are ionized by electron impact and further to an analyser with at least such an ion source and a particle energy analyser.